The present invention concerns a slab for cooling an upright furnace, especially a blast furnace, with a refractory lining. The slab is made of copper or a high-copper alloy and forged or rolled from ingot. Coolant channels in the form of vertical bores extend part-way through it.
Furnace-cooling slabs are usually inserted between the furnace's jacket and lining and communicate with its cooling system. The surface of the cooling elements facing the interior of the furnace are partly lined with a refractory material.
Cooling slabs with channels in the form of pipes immersed in cast iron are known. Due to the low heat conductivity of iron and to the resistance occasioned between the pipes and the mass of the slab by the layer of oxide or air gap, such plates do not remove much heat.
When the lining eventually wears out, the inner surface of the slabs will be directly exposed to the heat of the furnace. Since the temperature inside the furnace is much higher than the melting point of the iron and since the slab's inner heat-penetration resistance leads to unsatisfactory cooling of its hot surface, accelerated wear of the cast-iron slabs is inevitable, and the life of the furnace is limited.
Cast-copper slabs with coolant channels either comprising immersed pipes or directly left open in the casting. The structure of cast copper is not as homogeneous and dense as that of forged or rolled copper. The heat conduction of cast copper is accordingly less satisfactory and it is not as strong. Furthermore, the layer of oxide between the immersed pipes and the main mass of the copper inhibits heat conduction.
German 2 907 511 discloses a cooling slab forged or rolled from ingot, wherein the coolant channels are upright bores mechanically bored into the finished piece. The microstructure of this plate is essentially denser and more homogeneous than that of a cast-copper plate. There are none of the bubbles that frequently occur in cast copper. The slab is stronger and it conducts more heat more uniformly than a cast-copper plate will. The bores can be precisely positioned both vertically and horizontally, ensuring uniform heat removal.
The surface of the slab facing the interior of the furnace is lined with refractory brick or monolith. This approach reduces the slab's heating surface and, as the lining wears out or is lost, limits how much heat can be removed. Furthermore, the slab should be cooled thoroughly enough to maintain the temperature of its hot surface far below the softening point of copper.
Forged or rolled copper cooling slabs have a drawback, however, in that cooling is not ideal at the edges, and the joints between the monoliths or bricks between the plates cannot be kept cool enough.